The Conservative party is to break with convention on Wednesday with a party political broadcast appealing to voters to give money to charities working to relieve the drought in east Africa.

Ministers including George Osborne, Kenneth Clarke, Michael Gove, Cheryl Gillan and Andrew Mitchell are to deliver one-liners before switching tack, saying some things are more important than politics.

They will then describe the famine in Africa. At the end David Cameron will appear, saying all the people appearing in this broadcast have given money to relieve the famine in east Africa, before urging viewers to consider doing likewise.

It is understood that Steve Hilton, Cameron's strategy director and "blue sky thinker" is behind the idea.

He has long been turned off by the traditional party election broadcast, and has been an advocate of social action in which party politicians volunteer and donate.

Viewing figures for political broadcasts have shrunk as trust in politicians has declined.

All main parties are given airtime by broadcasters during the conference season, but the Tories have chosen to pass up the opportunity to transmit an overtly political message.

The broadcast, starting in the traditional wood-panelled room, will also deliberately avoid explicitly calling for viewers to vote Conservative or setting out criticisms of the Labour party.

The focus on aid to Africa could annoy those on the Tory right, who want aid spending cuts, but Cameron has been outspoken in defending the budget from its critics in the Daily Mail.

The unprecedented move is likely to be dismissed as a presentational stunt by critics, and it may also prove controversial if the party is accused of exploiting the famine to bolster its compassionate image.

Hilton encouraged Cameron to adopt a tree as the party's new logo and to boost its environmental credentials while in opposition. As part of that push, the future Tory leader was memorably filmed sledging with huskies at the north pole.

It was Cameron's determination to reposition the Tories that also prompted him to go ahead with a trip to Rwanda in 2007 when his Witney constituency was severely flooded.

Wednesday's broadcast is thought to be the first time a party political broadcast has been given over to a charitable cause.

Appeals for aid in cases of natural disasters are often broadcast on TV free of charge. Those appeals are organised by the Disasters Emergency Committee, an umbrella organisation representing charities.

Large parts of east Africa are facing the worst drought for 60 years, according to Oxfam.